The Main Problem is actually the phone, not the user
Android and iOS are at fault, here, not the user. Android in particular is a major data hog. The amount of data it uses in the background without your doing anything, is ridiculous. When I got my Galaxy Nexus, I used up more than 200 GB in three days just because of all the stuff that Android does in the background without user interaction. In particular, Google Play will automatically update your apps without your asking it, it is really easy to suddenly look at your phone and see the notice '8 apps updated', and if each app is 20 MB in size, you've just used 160 MB without knowing it. After only a few days, I had to change the settings to prevent 'background data use' or else I could have easily gone over my limit within the fir...
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